U.S. patent application number 15/517947 was filed with the patent office on 2018-09-20 for simultaneous evaluation of the volume and the position of voids in downhole cement.
The applicant listed for this patent is Halliburton Energy Services, Inc.. Invention is credited to Weijun GUO, Yike HU.
Application Number | 20180267200 15/517947 |
Document ID | / |
Family ID | 59225113 |
Filed Date | 2018-09-20 |
United States Patent
Application |
20180267200 |
Kind Code |
A1 |
HU; Yike ; et al. |
September 20, 2018 |
SIMULTANEOUS EVALUATION OF THE VOLUME AND THE POSITION OF VOIDS IN
DOWNHOLE CEMENT
Abstract
A method may comprise providing a wellbore penetrating a
subterranean formation, the wellbore being lined with a pipe and
having a cement between the pipe and the wellbore, wherein the
cement contains a defect; providing a control spectrum of gamma
radiation count rates as a function of energy for a control,
wherein the control comprises the cement without the defect;
emitting gamma rays into the pipe and the cement having the defect
from a source of a nuclear tool disposed in the wellbore; detecting
count rates of gamma radiation scattered back from the pipe and the
cement having the defect with a detector of the nuclear tool as a
function of energy to produce a sample spectrum; and deriving one
or more physical attributes related to the defect based on a
comparison of the sample spectrum and the control spectrum.
Inventors: |
HU; Yike; (Houston, TX)
; GUO; Weijun; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Halliburton Energy Services, Inc. |
Houston |
TX |
US |
|
|
Family ID: |
59225113 |
Appl. No.: |
15/517947 |
Filed: |
November 16, 2016 |
PCT Filed: |
November 16, 2016 |
PCT NO: |
PCT/US2016/062233 |
371 Date: |
April 7, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62272164 |
Dec 29, 2015 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01V 5/12 20130101; E21B
47/005 20200501 |
International
Class: |
G01V 5/12 20060101
G01V005/12; E21B 47/00 20060101 E21B047/00 |
Claims
1. A method comprising: providing a wellbore penetrating a
subterranean formation, the wellbore being lined with a pipe and
having a cement between the pipe and the wellbore, wherein the
cement contains a defect; providing a control spectrum of gamma
radiation count rates as a function of energy for a control,wherein
the control comprises the cement without the defect; emitting gamma
rays into the pipe and the cement having the defect from a source
of a nuclear tool disposed in the wellbore; detecting count rates
of gamma radiation scattered back from the pipe and the cement
having the defect with a detector of the nuclear tool as a function
of energy to produce a sample spectrum; and deriving one or more
physical attributes related to the defect based on a comparison of
the sample spectrum and the control spectrum.
2. The method of claim 1, wherein the defect is a void, wherein the
one or more physical attributes comprise a position of the void and
a volume of the void, and wherein deriving the one or more physical
attributes comprises: determining a high-energy range and an
intermediate-energy range for the gamma radiation; calculating a
count rate ratio (CR.sub.ratio) of the count rates of the sample
spectrum (CR.sub.sam) relative to the count rates for the control
spectrum (CR.sub.con) over the intermediate-energy range (IER)
according to CR ratio = CR sam CR con | IER ; ##EQU00003##
identifying a dipping point as an energy value corresponding to a
shape change in the sample spectrum relative to the control
spectrum in the high-energy range for the sample spectrum;
correlating the CR.sub.ratio and the dipping point using a known
dependence of the CR.sub.ratio and dipping point relative to the
position of the void and the volume of the void, thereby producing
a CR.sub.ratio/dipping point correlation; and determining the
volume and the position of the void in the cement based on the
CR.sub.ratio/dipping point correlation.
3. The method of claim 2, wherein correlating the CR.sub.ratio and
the dipping point involves plotting a monotonically increasing
extrapolation from the CR.sub.ratio and a monotonically decreasing
extrapolation from the dipping point on a void volume versus
position plot using the known dependence of the CR.sub.ratio and
dipping point on cement integrity for a given well completion
profile; and wherein determining the volume and the position of the
void is based on an intersection of the monotonically increasing
extrapolation from the CR.sub.ratio and the monotonically
decreasing extrapolation from the dipping point.
4. The method of claim 2 further comprising: establishing the known
dependence of the CR.sub.ratio and dipping point on the cement
integrity for the given well completion profile by computing the
CR.sub.ratio and the dipping point for a plurality of spectra
having the given well completion profile with differing volumes and
positions of cement voids.
5. The method of claim 4 further comprising: measuring the
plurality of spectra using a plurality of physically built
structures.
6. The method of claim 4 further comprising: measuring the
plurality of spectra using a plurality of computer simulated
structures.
7. The method of claim 2, wherein identifying the dipping point of
the spectrum uses a first derivative of the ratio of the control
spectrum and the sample spectrum.
8. The method of claim 2, wherein identifying the dipping point of
the spectrum uses a first derivative of a difference of the control
spectrum minus the sample spectrum.
9. The method of claim 1, wherein the defect is a void in the
cement and the one or more physical attributes comprises a percent
filling of the void with a liquid.
10. A method comprising: emitting gamma from a source of a nuclear
tool disposed in a wellbore to a pipe lining the wellbore and a
cement between the pipe and the wellbore, wherein the cement
contains a void; detecting count rates of gamma radiation scattered
back from the pipe and the cement having the void with a detector
of the nuclear tool as a function of energy to produce a sample
spectrum; and deriving two or more physical attributes related to
the defect based on a comparison of the sample spectrum and a
control spectrum, wherein the control spectrum is gamma radiation
count rates as a function of energy for a control that comprises
the cement without the void, wherein the control comprises the
cement without the void, and wherein the two or more physical
attributes comprise one or more selected from the group consisting
of a position of the void and a volume of the void.
11. The method of claim 10, wherein the two or more physical
attributes comprise the position of the void and the volume of the
void, and wherein deriving the two or more physical attributes
comprises: determining a high-energy range and an
intermediate-energy range for the gamma radiation; calculating a
count rate ratio (CR.sub.ratio) of the count rates of the sample
spectrum (CR.sub.sam) relative to the count rates for the control
spectrum (CR.sub.con) over the intermediate-energy range (IER)
according to CR ratio = CR sam CR con | IER ; ##EQU00004##
identifying a dipping point as an energy value corresponding to a
shape change in the sample spectrum relative to the control
spectrum in the high-energy range for the sample spectrum;
correlating the CR.sub.ratio and the dipping point using a known
dependence of the CR.sub.ratio and dipping point relative to the
position of the void and the volume of the void, thereby producing
a CR.sub.ratio/dipping point correlation; and determining the
volume and the position of the void in the cement based on the
CR.sub.ratio/dipping point correlation.
12. The method of claim 11, wherein correlating the CR.sub.ratio
and the dipping point involves plotting a monotonically increasing
extrapolation from the CR.sub.ratio and a monotonically decreasing
extrapolation from the dipping point on a void volume versus
position plot using the known dependence of the CR.sub.ratio and
dipping point on cement integrity for a given well completion
profile; and wherein determining the volume and the position of the
void is based on an intersection of the monotonically increasing
extrapolation from the CR.sub.ratio and the monotonically
decreasing extrapolation from the dipping point.
13. The method of claim 11 further comprising: establishing the
known dependence of the CR.sub.ratio and dipping point on the
cement integrity for the given well completion profile by computing
the CR.sub.ratio and the dipping point for a plurality of spectra
having the given well completion profile with differing volumes and
positions of cement voids.
14. The method of claim 13 further comprising: measuring the
plurality of spectra using a plurality of physically built
structures.
15. The method of claim 13 further comprising: measuring the
plurality of spectra using a plurality of computer simulated
structures.
16. A system comprising: a conveyance extending into a wellbore
penetrating a subterranean formation and coupled to a nuclear tool
having at least one source and at least one detector, wherein the
wellbore is lined with pipe and having a cement between the pipe
and the wellbore, wherein the cement contains a defect; and a
control system that includes a non-transitory medium readable by a
processor and storing instructions for execution by the processor
for the system to perform a method comprising: emitting gamma rays
into the pipe and the cement from a source of a nuclear tool
disposed in the wellbore; detecting count rates of gamma radiation
scattered back from the pipe and the cement having the defect with
a detector of the nuclear tool as a function of energy to produce a
sample spectrum; deriving one or more physical attributes related
to the defect based on a comparison of the sample spectrum and the
control spectrum.
17. The system of claim 16, wherein the defect is a void, wherein
the one or more physical attributes comprise a position of the void
and a volume of the void, and wherein deriving the one or more
physical attributes comprises: determining a high-energy range and
an intermediate-energy range for the gamma radiation; calculating a
count rate ratio (CR.sub.ratio) of the count rates of the sample
spectrum (CR.sub.sam) relative to the count rates for the control
spectrum (CR.sub.con) over the intermediate-energy range (IER)
according to CR ratio = CR sam CR con | IER ; ##EQU00005##
identifying a dipping point as an energy value corresponding to a
shape change in the sample spectrum relative to the control
spectrum in the high-energy range for the sample spectrum;
correlating the CR.sub.ratio and the dipping point using a known
dependence of the CR.sub.ratio and dipping point relative to the
position of the void and the volume of the void, thereby producing
a CR.sub.ratio/dipping point correlation; and determining the
volume and the position of the void in the cement based on based on
the CR.sub.ratio/dipping point correlation.
18. The system of claim 17, wherein identifying the dipping point
of the spectrum uses a first derivative of the ratio of the control
spectrum and the sample spectrum.
19. The system of claim 17, wherein identifying the dipping point
of the spectrum uses a first derivative of a difference of the
control spectrum minus the sample spectrum.
20. The system of claim 16, wherein the defect is a void in the
cement and the one or more physical attributes comprises a percent
filling of the void with a liquid.
Description
BACKGROUND
[0001] The present application relates to assessing the integrity
of a downhole cement.
[0002] Subterranean formation operations (e.g., stimulation
operations, sand control operations, completion operations, etc.)
often involve drilling a wellbore in a subterranean formation with
a drilling fluid (and thereafter placing a cement column between
the formation and a casing (or liner string) in the wellbore. The
cement column is formed by pumping a cement slurry through the
bottom of the casing and out through an annulus between the outer
casing wall and the formation face of the wellbore, or by directly
pumping a cement slurry into the annulus. The cement slurry then
cures in the annular space, thereby forming a column of hardened
cement that, inter alia, supports and positions the casing in the
wellbore and bonds the exterior surface of the casing to the
subterranean formation. This process is referred to as "primary
cementing."
[0003] Among other things, the cement column may keep fresh water
reservoirs from becoming contaminated with produced fluids from
within the wellbore. As used herein, the term "fluid" refers to
liquid phase fluids and gas phase fluids. The cement column may
also prevent unstable formations from caving in, thereby reducing
the chance of a casing collapse and/or stuck drill pipe. Finally,
the cement column forms a solid barrier to prevent fluid loss or
contamination of production zones. The degree of success of a
subterranean formation operation involving placement of a cement
column, therefore, depends, at least in part, upon the successful
cementing of the wellbore casing and the cement's ability to
maintain zonal isolation of the wellbore.
[0004] Failure of zonal isolation, among other things, may result
in environmental contamination, which may cause harm to both flora
and fauna, including humans. Such failure may further prevent
production or reduce the production capability of a wellbore, which
may result in abandonment. These issues may become exacerbated over
time, where an understanding of the state of the cement column at
an earlier point in time (e.g., the physical attributes of defects
in the cement) may allow remedial actions to be performed and
abandonment avoided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The following figures are included to illustrate certain
aspects of the embodiments, and should not be viewed as exclusive
embodiments. The subject matter disclosed is capable of
considerable modifications, alterations, combinations, and
equivalents in form and function, as will occur to those skilled in
the art and having the benefit of this disclosure.
[0006] FIG. 1 illustrates side view of a nuclear tool disposed in a
portion of a wellbore lined with a pipe and penetrating a
subterranean formation.
[0007] FIG. 2 is the spectra for (1) a cement without a void and
(2) a cement with a void.
[0008] FIG. 3 is a plot of the normalized sample spectrum minus the
normalized control spectrum used for determining a dipping point in
a high-energy range.
[0009] FIG. 4 is a plot of the dipping point values for a full set
of basis structures of different cement integrities.
[0010] FIG. 5 is a plot of the count rate ratios ratio for a full
set of basis structures of different cement integrities.
[0011] FIG. 6 is a void volume versus position plot with a
monotonically increasing extrapolation from the count rate ratio
and a monotonically decreasing extrapolation from the dipping
point.
DETAILED DESCRIPTION
[0012] The present application relates to assessing the integrity
of a downhole cement (e.g., the cement in the casing annulus of an
oil and gas wellbore), and more specifically, assessing the
physical attributes of defects in the cement using gamma radiation.
For example, the volume and radial position of defects like voids
in the downhole cement. Exemplary defects that may be present in a
cement may include, but not limited to voids, channels, or cracks
inside the cement sheath.
[0013] The voids that may be empty, at least partially filled with
gas (e.g., carbon dioxide for injection wells or formation gases),
at least partially filled with liquid (e.g., drilling mud or
formation fluids), or at least partially filled with gas and
liquid.
[0014] Embodiments of the present application analyze gamma ray
spectra to assess the integrity of a cement by deriving one or more
physical attributes of defects in the cement. Exemplary physical
attributes may include, but are not limited to, the volume of the
defect (e.g., the volume of a void or the percentage of porosity),
the radial position of the defect relative to the wellbore and/or a
pipe therein.
[0015] For example, FIG. 1 illustrates side view of a nuclear tool
100 disposed in a portion of a wellbore 102 lined with a pipe 104
(e.g., a casing) and penetrating a subterranean formation 106.
Disposed between the pipe 104 and the wellbore 102 is cement 108
having a defect therein, illustrated as a void 122. While
illustrated as a single pipe 104, in some instances, multiple pipes
104 may be lining the wellbore 102 with cement 108 therebetween,
one or more of which may have a void 122 therein. As used therein,
defining the cement 108 having a void 122 therein to be disposed
between the pipe 104 and the subterranean formation 106 does not
mean that the pipe 104 and the subterranean formation 106 are
necessarily the boundaries that contain the material 108. Rather,
the cement 108 having the void 122 therein is radially, relative to
the wellbore 102, located between the pipe 104 and the subterranean
formation 106. For example, the cement 108 having the void 122
therein may be contained by two pipes that themselves are disposed
between the pipe 104 and the subterranean formation 106. In another
example, the cement 108 having the void 122 therein may be
contained by the pipe 104 and a second pipe such that the second
pipe is disposed between the pipe 104 and the subterranean
formation 106.
[0016] The methods and systems described in more detail herein use
the nuclear tool 100 to determine a volume and position of the void
122 in the cement 108.
[0017] The illustrated nuclear tool 100 includes a housing 116 that
contains a source 110 and a detector 112. While the illustrated
nuclear tool 100 includes one source 110 and one detector 112, in
alternate embodiments, a nuclear tool may include more than one
source and more than one detector.
[0018] The nuclear tool 100 is coupled to a conveyance 114 that may
be used for moving the nuclear tool 100 along the wellbore 102,
providing power to the nuclear tool 100, communicating information
(e.g., data collected and operational commands), and the like, and
any combination thereof. Exemplary conveyances may include, but are
not limited to, a wireline, a coiled tubing, a slickline, a cable,
drill pipe (e.g., as part of a logging-while-drilling or
measuring-while-drilling tool), a downhole tractor, and the like.
The nuclear tool in FIG. 1 is positioned in the center of the
wellbore. In other embodiments, the nuclear tool could be pressed
against the wellbore wall or casing by an external support.
[0019] The source 110 (e.g., a .sup.137Cs source) emits gamma rays
118 into the pipe 104, the cement 108, and the formation 106. Gamma
radiation 120 scattered back from the pipe 104, the cement 108, and
the formation 106 is detected by the detector 112. Detection of the
gamma radiation 120 may be by way of measuring a count rate of
photons as a function of energy, which is referred to herein as a
spectrum.
[0020] Further, the nuclear tool 100 may be communicably coupled
126 (wired or wirelessly) to a controller 124. The controller may
communicate information to and/or from the nuclear tool 100. For
example, the controller 124 may receive data (e.g., count rates)
from the nuclear tool 100. In another example, the controller 124
may communicate instructions to the nuclear tool 100 regarding
operation of the nuclear tool 100 (e.g., when to take measurements
and the intensity of the gamma rays 118). Further, the controller
124 may perform the analyses and derivations described herein for
assessing the integrity of the cement and the physical attributes
of defects in the cement. Combinations of the foregoing may also be
implemented.
[0021] To derive the volume and the position or other physical
attributes of the void within the cement, a spectrum obtained from
a cement with unknown integrity (e.g., having a void or other
defect therein) is compared to a spectrum obtained from a standard
cement (e.g., a cement with no void). Generally, the composition
and surroundings (i.e., the pipe(s), the formation, and any cement
between additional pipes) for the control and sample cements should
be substantially the same. That is, the number, ordering, and
composition of layers (except for the defect) should be the
substantially the same when measuring the two spectra.
[0022] FIG. 2 is the spectra for (1) a cement without a defect
(referred to herein as the "control") and (2) a cement with a
defect, which is a void in this nonlimiting example (referred to
herein as the "sample"), which was achieved with a Monte-Carlo
N-particle simulation. These two plots may be analyzed and compared
to derive the physical attributes of the spectra. More
specifically, a count rate ratio and a dipping point, both detailed
below, may be used to ascertain the volume and the position of the
void.
[0023] First, the count rate ratio is related to the sum of count
rates at an intermediate-energy range along the spectrum (e.g., 100
keV (kilo electron volt) to 300 keV and any subset thereof). The
count rate ratio (CR.sub.ratio) may be defined as the ratio between
a sample spectrum count rate (CR.sub.sam) and a control spectrum
count rate (CR.sub.con) at the selected intermediate-energy range
(IER) (e.g., about 150 key to about 250 key), which, for example,
may be expressed mathematically by Equation 1.
CR ratio = CR sam CR con | IER Equation 1 ##EQU00001##
[0024] Second, the dipping point is related to the differences
between the sample and control spectra within a high-energy range
(e.g., about 300 key to about 500 key). More specifically, the
dipping point is the energy value corresponding to the spectrum
shape change within a high-energy range. The sample spectrum and
corresponding control spectrum (or equivalent derivatives thereof)
may first be normalized. For example, each spectrum may be
normalized so that the total count rates for each spectrum is 1.
Then, the normalized control spectrum may be subtracted from the
normalized sample spectrum. Continuing with the earlier example,
the spectra illustrated in FIG. 2 once normalized and subtracted
provide FIG. 3, which reveals the differences in the two spectra in
the high-energy range. The "dipping point," labelled in FIG. 3,
refers to the energy value corresponding to the minimum point in
the normalized spectrum difference (i.e., normalized sample
spectrum minus the normalized control spectrum) within the
high-energy range. The dipping point may alternatively be
determined using first derivatives of the normalized sample and
control spectra, where once subtracted the dipping point is defined
as the energy value corresponding to where the first derivative
spectrum difference is zero when transitioning from negative to
positive.
[0025] While this example specifically uses the normalized sample
spectrum minus the normalized control spectrum (or derivatives
thereof), the dipping point may be determined by other mathematical
manipulations that compare the normalized sample spectrum to the
normalized control spectrum to ascertain the differences in the
high-energy range and, more specifically, the shape change in the
high-energy range. For example, the normalized control spectrum
minus the normalized sample spectrum (or derivatives thereof) may
be used. Alternatively, a ratio of the two normalized spectra (or
derivatives thereof) may be used.
[0026] Additionally, while the spectrum was normalized in this
example, the dipping point could be determined by mathematical
manipulations that compare the sample spectrum to the control
spectrum to ascertain the difference in the high energy range and,
more specifically, the shape change in the high energy range.
[0027] Further, the illustrated high and intermediate-energy ranges
are not limiting. Methods and analyses described herein may involve
determining the high and intermediate-energy ranges. Generally, the
intermediate-energy range is non-overlapping with the high-energy
range and at a lower energy than the high-energy range. The
high-energy range may be adjusted (e.g., 250 key to 600 key and any
subset thereof) so that the lower limit of the high-energy range is
preferable at a higher energy than the peak energy of the original
spectra. The intermediate-energy range may be adjusted (e.g., 75
key to 300 key and any, subset thereof) so that the
intermediate-energy range preferably encompasses the peak energy of
the spectra. The starting and ending values for each of the
intermediate- and high-energy ranges are tool type specific and can
be determined using computer simulation or lab experiments.
[0028] The dependence of count rate ratio and dipping point on the
volume and the position of the void for a particular wellbore
completion profile can be found by generating the spectra from a
series of cement structure with different integrities using either
computer simulated structures with simulated measurements or
physically built structures with in-lab measurements. The
structures are considered as the basis structures, which consist of
different amount of void (from 10% up to 90% of the annular space)
at different position inside the annular space. The position was
labeled as 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.
Position 0 is defined as the inner surface of the void coincides
with the outer surface of the casing, and position 1 is defined as
the inner surface of the void coincides with the outer surface of
the annular space. Expanding on the example illustrated in FIGS.
2-3, the Monte-Carlo N-particle simulation was used to simulate the
spectra for all basis structures. For the same wellbore completion
profile (i.e., the same configuration of the pipe, cement, and
wellbore) as FIG. 2, the dipping points from all basis structures
are plotted in FIG. 4, and the count rate ratio from all basis
structures are plotted in FIG. 5. Although 10% is chosen as the
incremental amount for the basis structures of void amount, any
number between 0% and 100% can be used when generating a series of
structures of different void amounts. Similarly, although 0.1 is
chosen as the incremental amount for the basic structure of void
position, any number between 0 and 1 can be used when generating a
series of structures of different void position.
[0029] Both the volume and the position of the void affects the
count rates in the intermediate energy range. More specifically,
count rates increase in the intermediate-energy range as the volume
of the void increases and the void is closer to the tool (i.e.,
closer to the pipe). Therefore, a small void volume at a position
close to the pipe could have the same count rate ratio as a large
void volume at position farther away from the pipe.
[0030] Therefore, the count rate ration and the dipping point may
be correlated, for example, to produce a count rate ration/dipping
point correlation that may be used to determine the volume and
position of the void in the cement. For example, for a given count
rate ratio value, an equal-rate ratio curve can be extrapolated
(e.g., as a monotonically increasing curve) within a void volume
vs. position plot, as illustrated in FIG. 6.
[0031] Further, the energy of the dipping point decreases as the
volume of the void increases and the void is farther from the pipe.
Therefore, a large cement void volume at void position close to the
pipe could have the same dipping point value as that of a small
cement void volume at a farther distance from the pipe. For a given
dipping point value, an equal-dipping point curve can be
extrapolated (e.g., as a monotonically decreasing curve) within a
void volume vs. position plot, as illustrated in FIG. 6.
[0032] Generally, the method described herein include obtaining a,
control spectrum for a given well completion profile by lab
measurement, computer simulation, or a downhole measurement in good
bonding section. Then, the measured sample spectrum from a cement
structure with the void is compared to the control spectrum to
determine a count rate ratio and dipping point value. Finally, the
volume and the position of the void within the cement can be
determined from a FIG. 6 plot where the equal-dipping point
extrapolation and the equal-count rate ratio extrapolations are
obtained from FIGS. 4-5. In FIG. 6, the intersection of the
equal-count rate ratio and equal-dipping point extrapolations gives
rise to the void position and void volume inside the cement.
[0033] Other physical characteristics of defects in the cement
including, but not limited to those described herein, may be
derived from a comparison of the sample spectrum and the control
spectrum.
[0034] In some embodiments, a control system may include a set of
instructions on a processor that cause a processor and/or system
coupled thereto to perform the analyses, correlations, and methods
described herein. In some instances, the control system (e.g.,
control system 124) may be a singular component of a system. In
some instances, the control system (e.g., control system 124) may
include several processors communicably coupled but not necessarily
in a singular component. For example, data may be collected and
stored on a first processor in the nuclear tool, and a second
processor located outside the wellbore may be coupled to the first
processor where the second processor performs analyses described
herein on the data.
[0035] The processor may be a portion of computer hardware used to
implement the various illustrative blocks, modules, elements,
components, methods, and algorithms described herein. The processor
may be configured to execute one or more sequences of instructions,
programming stances, or code stored on a non-transitory,
computer-readable medium. The processor can be, for example, a
general purpose microprocessor, a microcontroller, a digital signal
processor, an application specific integrated circuit, a field
programmable gate array, a programmable logic device, a controller,
a state machine, a gated logic, discrete hardware components, an
artificial neural network, or any like suitable entity that can
perform calculations or other manipulations of data. In some
embodiments, computer hardware can further include elements such
as, for example, a memory (e.g., random access memory (RAM), flash
memory, read only memory (ROM), programmable read only memory
(PROM), erasable programmable read only memory (EPROM)), registers,
hard disks, removable disks, CD-ROMS, DVDs, or any other like
suitable storage device or medium.
[0036] Executable sequences described herein can be implemented
with one or more sequences of code contained in a memory. In some
embodiments, such code can be read into the memory from another
machine-readable medium. Execution of the sequences of instructions
contained in the memory can cause a processor to perform the
process steps described herein. One or more processors in a
multi-processing arrangement can also be employed to execute
instruction sequences in the memory. In addition, hard-wired
circuitry can be used in place of or in combination with software
instructions to implement various embodiments described herein.
Thus, the present embodiments are not limited to any specific
combination of hardware and/or software.
[0037] As used herein, a machine-readable medium will refer to any
medium that directly or indirectly provides instructions to the
processor for execution. A machine-readable medium can take on many
forms including, for example, non-volatile media, volatile media,
and transmission media. Non-volatile media can include, for
example, optical and magnetic disks. Volatile media can include,
for example, dynamic memory. Transmission media can include, for
example, coaxial cables, wire, fiber optics, and wires that form a
bus. Common forms of machine-readable media can include, for
example, floppy disks, flexible disks, hard disks, magnetic tapes,
other like magnetic media, CD-ROMs, DVDs, other like optical media,
punch cards, paper tapes and like physical media with patterned
holes, RAM, ROM, PROM, EPROM and flash EPROM.
[0038] Embodiments described herein include, but are not limited
to, Embodiment A, Embodiment B, Embodiment C, and Embodiment D.
[0039] Embodiment A is a method comprising: providing a wellbore
penetrating a subterranean formation, the wellbore being lined with
a pipe and having a cement between the pipe and the wellbore,
wherein the cement contains a defect; providing a control spectrum
of gamma radiation count rates as a function of energy for a
control, wherein the control comprises the cement without the
defect; emitting gamma rays into the pipe and the cement having the
defect from a source of a nuclear tool disposed in the wellbore;
detecting count rates of gamma radiation scattered back from the
pipe and the cement having the defect with a detector of the
nuclear tool as a function of energy to produce a sample spectrum;
and deriving one or more physical attributes related to the defect
based on a comparison of the sample spectrum and the control
spectrum.
[0040] Embodiment B is a system comprising: a conveyance extending
into a wellbore penetrating a subterranean formation and coupled to
a nuclear tool having at least one source and at least one
detector, wherein the wellbore is lined with pipe and having a
cement between the pipe and the wellbore, wherein the cement
contains a defect; and a control system that includes a
non-transitory medium readable by a processor and storing
instructions for execution by the processor for the system to
perform a method of Embodiment A.
[0041] Embodiments A and B may optionally include one or more of
the following: Element 1: wherein the defect is a void, wherein the
one or more physical attributes comprise a position of the void and
a volume of the void, and wherein deriving the one or more physical
attributes comprises: determining a high-energy range and an
intermediate-energy range for the gamma radiation; calculating a
count rate ratio (CR.sub.ratio) of the count rates of the sample
spectrum (CR.sub.sam) relative to the count rates for the control
spectrum (CR.sub.con) over the intermediate-energy range (IER)
according to CR.sub.ratio=CR.sub.sam/CR.sub.com|.sub.IER;
identifying a dipping point as an energy value corresponding to a
shape change in the sample spectrum relative to the control
spectrum in the high-energy range for the sample spectrum;
correlating the CR.sub.ratio and the dipping point using a known
dependence of the CR.sub.ratio and dipping point relative to the
position of the void and the volume of the void, thereby producing
a CR.sub.ratio/dipping point correlation; and determining the
volume and the position of the void in the cement based on the
CR.sub.ratio/dipping point correlation; Element 2: Element 1 and
wherein correlating the CR.sub.ratio and the dipping point involves
plotting a monotonically increasing extrapolation from the
CR.sub.ratio and a monotonically decreasing extrapolation from the
dipping point on a void volume versus position plot using the known
dependence of the CR.sub.ratio and dipping point on cement
integrity for a given well completion profile; and wherein
determining the volume and the position of the void is based on an
intersection of the monotonically increasing extrapolation from the
CR.sub.ratio and the monotonically decreasing extrapolation from
the dipping point; Element 3: Element 1 and the method further
comprising: establishing the known dependence of the CR.sub.ratio
and dipping point on the cement integrity for the given well
completion profile by computing the CR.sub.ratio and the dipping
point for a plurality of spectra having the given well completion
profile with differing volumes and positions of cement voids;
Element 4: Element 3 and the method further comprising: measuring
the plurality of spectra using a plurality of physically built
structures; Element 5: Element 3 and the method further comprising:
measuring the plurality of spectra using a plurality of computer
simulated structures; Element 6: Element 1 and wherein identifying
the dipping point of the spectrum uses a first derivative of the
ratio of the control spectrum and the sample spectrum; Element 7:
Element 1 and wherein identifying the dipping point of the spectrum
uses a first derivative of a difference of the control spectrum
minus the sample spectrum; and Element 8: wherein the defect is a
void in the cement and the one or more physical attributes
comprises a percent filling of the void with a liquid. Exemplary
combinations may include, but are not limited to: Element 1 and 2
in combination with Element 6 and/or 7; Element 1 and 3 in
combination with Element 6 and/or 7 and optionally Element 4 or 5;
and Element 1 in combination with Element 8.
[0042] Embodiment C is a method comprising: emitting gamma from a
source of a nuclear tool disposed in a wellbore to a pipe lining
the wellbore and a cement between the pipe and the wellbore,
wherein the cement contains a void; detecting count rates of gamma
radiation scattered back from the pipe and the cement having the
void with a detector of the nuclear tool as a function of energy to
produce a sample spectrum; and deriving two or more physical
attributes related to the defect based on a comparison of the
sample spectrum and a control spectrum, wherein the control
spectrum is gamma radiation count rates as a function of energy for
a control that comprises the cement without the void, wherein the
control comprises the cement without the void, and wherein the two
or more physical attributes comprise one or more selected from the
group consisting of a position of the void and a volume of the
void.
[0043] Embodiment D is a system comprising: a conveyance extending
into a wellbore penetrating a subterranean formation and coupled to
a nuclear tool having at least one source and at least one
detector, wherein the wellbore is lined with pipe and having a
cement between the pipe and the wellbore, wherein the cement
contains a defect; and a control system that includes a
non-transitory medium readable by a processor and storing
instructions for execution by the processor for the system to
perform a method of Embodiment C.
[0044] Embodiments C and D may optionally include one or more of
the following: Element 9: wherein the two or more physical
attributes comprise the position of the void and the volume of the
void, and wherein deriving the two or more physical attributes
comprises: determining a high-energy range and an
intermediate-energy range for the gamma radiation; calculating a
count rate ratio (CR.sub.ratio) of the count rates of the sample
spectrum (CR.sub.sam) relative to the count rates for the control
spectrum (CR.sub.con) over the intermediate-energy range (IER)
according to
CR ratio = CR sam CR con | IER ; ##EQU00002##
identifying a dipping point as an energy value corresponding to a
shape change in the sample spectrum relative to the control
spectrum in the high-energy range for the sample spectrum;
correlating the CR.sub.ratio and the dipping point using a known
dependence of the CR.sub.ratio and dipping point relative to the
position of the void and the volume of the void, thereby producing
a CR.sub.ratio/dipping point correlation; and determining the
volume and the position of the void in the cement based on the
CR.sub.ratio/dipping point correlation;
[0045] Element 10: Element 9 and wherein correlating the
CR.sub.ratio and the dipping point involves plotting a
monotonically increasing extrapolation from the CR.sub.ratio and a
monotonically decreasing extrapolation from the dipping point on a
void volume versus position plot using the known dependence of the
CR.sub.ratio and dipping point on cement integrity for a given well
completion profile; and wherein determining the volume and the
position of the void is based on an intersection of the
monotonically increasing extrapolation from the CR.sub.ratio and
the monotonically decreasing extrapolation from the dipping
point;
[0046] Element 11: Element 9 and the method further comprising:
establishing the known dependence of the CR.sub.ratio and dipping
point on the cement integrity for the given well completion profile
by computing the CR.sub.ratio and the dipping point for a plurality
of spectra having the given well completion profile with differing
volumes and positions of cement voids;
[0047] Element 12: Element 11 and further comprising: measuring the
plurality of spectra using a plurality of physically built
structures;
[0048] Element 13: Element 11 and further comprising: measuring the
plurality of spectra using a plurality of computer simulated
structures. Exemplary combinations may include, but are not limited
to; Elements 9 and 10 in combination; and Elements 9 and 11 in
combination with Element 12 and/or element 13.
[0049] Unless otherwise indicated, all numbers expressing
quantities of ingredients, properties such as molecular weight,
reaction conditions, and so forth used in the present specification
and associated claims are to be understood as being modified in all
instances by the term "about." Accordingly, unless indicated to the
contrary, the numerical parameters set forth in the following
specification and attached claims are approximations that may vary
depending upon the desired properties sought to be obtained by the
embodiments of the present invention. At the very least, and not as
an attempt to limit the application of the doctrine of equivalents
to the scope of the claim, each numerical parameter should at least
be construed in light of the number of reported significant digits
and by applying ordinary rounding techniques.
[0050] One or more illustrative embodiments incorporating the
invention embodiments disclosed herein are presented herein. Not
all features of a physical implementation are described or shown in
this application for the sake of clarity. It is understood that in
the development of a physical embodiment incorporating the
embodiments of the present invention, numerous
implementation-specific decisions must be made to achieve the
developer's goals, such as compliance with system-related,
business-related, government-related and other constraints, which
vary by implementation and from time to time. While a developer's
efforts might be time-consuming, such efforts would be,
nevertheless, a routine undertaking for those of ordinary skill in
the art and having benefit of this disclosure.
[0051] While compositions and methods are described herein in terms
of "comprising" various components or steps, the compositions and
methods can also "consist essentially of" or "consist of" the
various components and steps.
[0052] Therefore, the present invention is well adapted to attain
the ends and advantages mentioned as well as those that are
inherent therein. The particular embodiments disclosed above are
illustrative only, as the present invention may be modified and
practiced in different but equivalent manners apparent to those
skilled in the art having the benefit of the teachings herein.
Furthermore, no limitations are intended to the details of
construction or design herein shown, other than as described in the
claims below. It is therefore evident that the particular
illustrative embodiments disclosed above may be altered, combined,
or modified and all such variations are considered within the scope
and spirit of the present invention. The invention illustratively
disclosed herein suitably may be practiced in the absence of any
element that is not specifically disclosed herein and/or any
optional element disclosed herein. While compositions and methods
are described in terms of "comprising," "containing," or
"including" various components or steps, the compositions and
methods can also "consist essentially of" or "consist of" the
various components and steps. All numbers and ranges disclosed
above may vary by some amount. Whenever a numerical range with a
lower limit and an upper limit is disclosed, any number and any
included range falling within the range is specifically disclosed.
In particular, every range of values (of the form, "from about a to
about b," or, equivalently, "from approximately a to b," or,
equivalently, "from approximately a-b") disclosed herein is to be
understood to set forth every number and range encompassed within
the broader range of values. Also, the terms in the claims have
their plain, ordinary meaning unless otherwise explicitly and
clearly defined by the patentee. Moreover, the indefinite articles
"a" or "an," as used in the claims, are defined herein to mean one
or more than one of the element that it introduces.
* * * * *